On Friday, March 6, 2020 at 7:51:10 PM UTC-6, Brent wrote:
>
>
>
> On 3/6/2020 3:55 PM, Bruce Kellett wrote:
>
> On Sat, Mar 7, 2020 at 10:17 AM John Clark <[email protected]
> <javascript:>> wrote:
>
>> This video just went online, I thought it was excellent:
>>
>> Parallel Worlds Probably Exist. Here’s Why
>> <https://www.youtube.com/watch?v=kTXTPe3wahc>
>>
>> John K Clark
>>
>
> Impressive graphics, but the same old....same old....
>
> Bruce
>
>
> You might find this interview of Sean Carroll more interesting. He's
> aware of the problems with MWI and is fairly candid about it even though he
> likes it. Start at 54:00 to skip all the explanation of QM.
> https://www.youtube.com/watch?v=XjDiOu5__oA
>
> Brent
>
The question on whether QM has an infinite or finite Hilbert space can be
addressed with the existence of event horizons. The cosmological event
horizon puts a limit. Consider a Planck scale quantum state that has been
redshifted to the cosmological horizon scale. This is a ratio of around
10^{60} and from the FLRW this leads to a distance of around 1800 billion
light years. Since this defines a finite region this means the Hilbert
space accessible to any observer is finite, even if enormously large. Even
if the global Hilbert space is infinite, observers are fundamentally local
and the amount of quantum information accessible is finite. To take this
further, with inflationary cosmology the cosmological event horizon on the
high energy vacuum was only 10^2 or 10^3 Planck units of radius the large
number of quantum states that appear accessible on the low energy physical
vacuum are an enormous redundancy.
At around 1:14 Carroll gets to brass-tacks on this issue with the horn. The
idea in MWI is then "everything happens that can happen," which some people
find difficult. In effect even though there is a probability weight with
each possible branch, an observer that witnesses a highly improbable
quantum event has this sense they are on a split branch and have no post
collapse information about a prior probability. MWI has the concept of a
cosmic wave function, but this sense of there being only two outcomes
reflects a lack of counterfactual definite reasoning tied to objective
probabilities. As a result these branches occur in a certain nonlocal
sense.
Is this at all demonstrable? No, counterfactual definite reasoning and the
existence of a global wave are not demonstrable. There are forms of
horizons, in general a form of epistemic horizon, which are a
generalization of the inaccessibility of information in QM and with general
relativity and event horizons. So whether there is or is not a global
cosmological wave function is a metaphysical choice of an analyst.
Generally ψ-ontological interpretations have a global cosmic wave function,
but a subset of those with a hidden variable interpretation also have
counterfactualism.
As Carroll points out there are four major types of interpretations, MWI
and deBroglie-Bohm, both ψ-ontic but with and without counterfactualism,
and Qubism and dynamic collapse that are ψ-epistemic. Qubism has some
advantages, but it leads to odd ideas that are almost solipsism. Dynamic
collapse and related idea of stochastic QM have wave functions just
spontaneously collapse and the more entangled the system is the more
frequent this will happen. I have certain issues there with how to treat
coherent states such as with lasers or with condensates of states. In
general one can pick and choose, and these are available for those who want
to think of certain problems in a certain framework. I think frankly that
QM decoherence, and by extension a measurement, amounts to a sort of Gödel
numbering of quantum bits by quantum bits. I see all of these
interpretations of QM then as a sort of incompleteness or inconsistency
that results by trying to impose a certain question or proposition on QM
that is not decidable.
LC
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